1. Field of the Invention
The invention is generally related to the alignment and spacing of tubes in heat exchangers and more particularly to improved means for maintaining alignment and spacing between tubes.
2. General Background
In superheater units, tubes are heated to impart additional energy to the saturated vapor contained in the tubes. Temperature differentials in the stream of hot gases are a potentially significant cause of premature tube failure. Failures occur as a result of the differential expansion of the tube metal from tube-to-tube within a unit. Temperature differences cause the tubes to shift out of their original positions, producing stresses, metal fatigue, and tube misalignment. Tube misalignment leads to further increase in stress as well as erosion when tubes shift out of alignment into the path of hot gases. In superheaters, the heat exchange tubes are arranged parallel to each other and extend vertically through the superheater. One means of maintaining tube alignment has been through the use of tongue and groove ties. A tongue welded to one tube has a flange at one end that is received in a groove defined by two pieces welded to an adjacent tube. This type of arrangement presents problems of at least two types. One is that welding is required on both tubes. The second is that if the tongue or groove weld fails, metal is likely to be pulled from the tube. This weakens the tube and increases the likelihood of a tube leak.